1. Field of the Invention
The present invention is directed toward a fan for use in cooling circuitry found in electronic equipment. More particularly, the present invention provides a highly accurate and highly temperature-sensitive electronic cooling fan capable of responding in real time to minor fluctuations in ambient temperature of the region or device to be cooled using cost-effective moderate to low tolerance componentry without resorting to circuit trimming or discarding a large number of units.
2. Description of the Related Art
Modern electronic devices have a tendency to retain heat when operated for long periods of time, which eventually interferes with proper function of the equipment. Internal cooling systems, such as fans, are therefore required to maintain system integrity and assure proper performance. Cooling fans, however, introduce their own set of drawbacks—most notably among them unwanted noise and unnecessary power consumption. These drawbacks are particularly acute when the fan is required either to run at a single speed or to remain off. To overcome such drawbacks, a variable-speed fan was conceived.
Even designs for variable-speed fans, however, present difficulties in measuring with sufficient accuracy the temperature of the area or circuit to be cooled. Calibrating measurements over a wide range of temperatures can be difficult and costly—particularly considering that the measurement circuit's componentry is often manufactured to moderate or low tolerances for the sake of cost savings. A continuous-variable speed fan capable of calibrating temperature measurements across a wide temperature range in a highly cost-effective manner was therefore conceived.
Related art falls into two broad categories: fans with speed control, and calibration means for sensor equipment.
Fans with Speed Control.
The related art regarding fans with speed control includes an intelligent fan system including a microcontroller with memory and an interface to a host computer system including a temperature sensing device connected thereto. Via a communication signal, the microcontroller adjusts the fan motor's rotation speed according to a plurality of control instructions in response to a detected temperature using a speed-temperature curve stored in memory. Each controller is fan specific, i.e., the host machine programs a specific external fan controller board to control a specific fan. Matching appropriate voltage to temperature input and subsequent fan motor rotation is accomplished by programming each of the external fan controllers at the time of manufacture.
The related art also discloses a cooling-fan speed control for use with computers. In auto mode after detecting system configuration, cooling-fan start speeds are retrieved into the system controller from a fan-speed table stored in memory. During operation, cooling-fan speed is increased or decreased in response to the temperature sensed by an ambient air temperature sensor. During manufacturing, an appropriate fan-speed table is written into a controller's memory, and easily rewritten at any time to reflect changes in data.
Also disclosed in the related art is a microprocessor-controlled fan for cooling architectural spaces, such as rooms, within buildings or other dwellings. The fan has a motor responsive to a control signal and excited by a power source having first and second terminals and a first predetermined frequency. The system entails means for selecting a desired temperature and providing a first electrical signal representative thereof, means for sensing an actual temperature and providing a second electrical signal representative thereof, and means, preferably a microprocessor, for receiving, sampling and interpreting the first and second electrical signals. The microprocessor then controls the speed of the fan with respect to the magnitude of the difference measured.
Also available is a system that drives an indoor blower of a heating, ventilating, and air conditioning (HVAC) unit using a system-control signal for determining the air-flow rate of the HVAC by controlling the speed or torque of a motor driving an indoor blower. A microprocessor, with optional analog-to-digital codec and programmable non-volatile (PVN) memory, controls operation of the motor using motor-control signals according to various system parameters, which can be stored in the PVN. The motor-control signals are provided to the electrically commutated motor (ECM) for speed or torque control via the microprocessor in response to a number of system-control signals provided by the system control such as a temperature signal provided by a thermostat. The microprocessor defines an operating mode for the ECM in response to the system control signal. A system controller such as a thermostat activates air conditioning demand to instruct the motor to operate at a speed or torque to drive a fan to deliver a defined air flow for a period of time.
Calibration of Sensor Equipment.
The technology of sensor equipment also discloses a method of calibrating analog sensor measurements in a computer system. A calibrated measurement is created by comparing an analog sensor measurement, such as temperature (either ambient or of particular circuit components) or voltage, to a calibration curve generated by reading from memory two curve-defining values (such as slope and intercept) from a set of such values stored during the manufacturing process. The results of at least two reference sensor measurements, taken during the manufacturing process, are compared against a calibrated scale and then used to calibrate potentially inaccurate in-system analog sensor measurements via a linear algorithm using the initially calibrated values. During operation, a calibrated result is calculated using the analog sensor measurement result and the values that define the curve read from the memory device. During the manufacturing process, each temperature measurement is taken by first bringing the ambient temperature within the computer chassis to a known, calibrated temperature and then performing a sensor measurement operation.
The related art also discloses a microprocessor-controlled fan for cooling architectural spaces, such as rooms, within buildings or other dwellings. The fan comprises a motor responsive to a control signal and excited by a power source having first and second terminals and a first predetermined frequency. The system comprises means for selecting a desired temperature and providing a first electrical signal representative thereof, means for sensing an actual temperature and providing a second electrical signal representative thereof, and means, preferably a microprocessor, for receiving, sampling and interpreting the first and second electrical signals. The microprocessor then controls the speed of the fan with respect to the magnitude of the difference measured.
The related art also discloses a device for indicating refrigerant temperature by connecting a thermistor to an electronic controller that continually measures changes in the resistance of the thermistor, and in turn, drives a compressor clutch and condenser. The thermistor is calibrated at installation by measuring the resistance of the thermistor when constant-temperature air is flowing thereover and then comparing the value measured with a standard value. A correction factor based upon the comparison can then be stored in a non-volatile memory, either within a microcomputer or on external media, for use in later calibrations. For calibration, constant-temperature air is flowed over the thermistor, preferably at 25° C., and the thermistor is operated at a low level of self heat. After stabilization, the resistance of the thermistor is measured and compared with a known standard or nominal value. The results of the comparison are stored in the microprocessor in a non-volatile memory or external memory such as a non-volatile memory, and later used as a correction factor during operation of the control system. When the calibration signal is generated, the microprocessor compares the measured thermistor resistance with a nominal value stored on a look-up table, and then stores the difference as a correction factor in the non-volatile memory of the microprocessor or an external memory such as a non-volatile memory.